Visual perception and action Flashcards
Whats perception?
The sensory experience of the world. It involves both recognizing environmental stimuli and actions in response to these stimuli.
What do we gain through the perceptional process?
we gain information about the properties and elements of the environment that are critical to our survival.
2 things perception lets us do
creates our experience of the world around us;
it allows us to act within our environment.
how we receive info from the environment?
we are equipped with five sensory organs (eyes, ears, nose, mouth, touch)
Each receives raw sensory input from the external world that it transmits it to the brain
what can perception be thought as?
as the basic cognitive process that analyzes and makes sense of information from the sens
whats sensation?
The ability of our senses to detect various forms of energy (light or sound waves for example)
To sense does not involve making sense of the input.
whats perception?
Making sense of the raw sensory input
where is info transmitted down from? and to where?
visual cortex (back of the brain) to two relatively independent visual pathways
what are these pathways called?
The ventral (or “what”) pathway is responsible for processing colour and form•
The dorsal (“where”) pathway is responsible for movement and spatial relations
What was historically thought of what the visual system provided us with?
an internal (and conscious) representation of the external world (allowing us to recognize)
what did rival theorists suggest instead?
suggested the aim of the visual system was to facilitate our interaction with the world
what did Milner & Goodale (1995; 2008) instead argue for?
two visual systems each fulfilling a different function:
- One which is focused on providing an internal representation of the world;
- One that is focused on action and interaction with the world
What’s the vision for the perception stream? Milner & Goodale (1995; 2008)
based on the ventral stream. Used to decide whether an object is a cat, or a buffalo or when admiring a landscape. Role – to identify objects
What’s a Vision-for-action system? Milner & Goodale (1995; 2008)
based on the dorsal stream and used for visually guided action (i.e., interactions with the environment)
What’s bottom-up processing in perception?
Physical characteristics of stimuli drive perception (in other words, top-down processing is not needed for perception, the stimulus is enough).
Top-down processing in perception:
Knowledge, expectations, thoughts, past experiences guide perception (in other words, the stimulus is not enough, we must work on the image arriving on the retina to make sense of it)
Gibson’s(1979) Theory of Direct Perception
- vision for action - what approach?
Primarily bottom-up
Gregory’s(1970) Constructivist Theory of Perception
-visison for recognition
primarily top-down
Milner & Goodale’s(1998) Perception-Action Mode
- vision for recognition and action
Both top-down and bottom up
Gibsons theory of direction perception
- whats bottom up?
whats action driven?
bottom-up: Perception takes place directly from the environmental input. There is no need to work on the image arriving on the retina (i.e., no top-down processing required)
•Action driven: The end point (or purpose) of perception is to enable interactions with the real word
what did gibson argue?
that vision developed so our ancestors could respond rapidly to the environmen
what type of apporach did gibson go with?
An Ecological Approach:
•Perception should be studied by determining how the real environment structures the light that reaches our retina (the ambient optic array, described next)•
He did not agree with laboratory based investigations of perception using images (often line drawings) presented in a 2D plane
how do we take useful info about the environment?
about the environment directly from the light waves that reach our eyes
- Important theory elements:
- Ambient optic array
- Invariants
- Optic Flow
- Affordances
Whats the ambient optic array?
Structure is imposed on light waves that are refracted by the textured surfaces in the world around us.
- The light reflected from surfaces in the environment converges at the point in space occupied by the observer.
- As you move, the position of your head with respect to the environment is altered and the optic array changes accordingly.
Whats invariants?
Invariants
•Higherorder features of the environment that provide unambiguous information as to its nature.
•Essentially invariants are things that don’t change (remain stable) as we move through our environment that give us useful information about that movement
- Examples:
- Horizon
- Texture Gradient
What can texture gradients (invariants) tell us?
Textures can tell us if a surface is receding because density elements (the number per square meter) increase with distance
•Where texture is missing, there can be ambiguity about shape and orientation…think of the Illusions from earlier. •Powerful source of invariant information about the distance, size and orientation of surfaces in the environment
Whats optic flow?
Optic Flow
- Motion is critical to Gibson’s view
- In a static view of the environment, all information is invariant because it never changes.
•To perceive and make use of invariant information, we have to see the environment change over time (i.e., as we move)
whats optic flow?
whats flow pattern?
changes in the light hitting the eye (from the ambient optic array) results from motion
give critical information about what is going on in the environment
what happens Iif you are travelling forwards, the point to which you are heading is known as….
focus of expansion (AKA the pole).
movement of the focus of expansion?
and the flow pattern?
remains static and everything else moves relative to it (causing the flow pattern)•
The flow pattern is such that the texture elements appear to be radiating from the direction in which you are heading.
evidence for gibsons theory -
Bruggeman, Zosh & Warren (2007)
Tested the importance of optic flow patterns directly
•They put participants in a virtual reality environment
- Participants had to adapt to walking with a virtual heading direction displaced 10 degrees from their actual walking direction.
- They were then tested again with a normally aligned heading.
- The visual environment either provided rich optic flow, or sparse optic flow.
•FOUND: adaptation of the walking path was more rapid and complete in the structured environment
.•The negative aftereffect on path deviation was twice that in the sparse environment showing the importance of optic flow information.
evidence pt 2 Wang et al 2012
- Simulated the pattern of optic flow that would be experienced if individuals moved forward in a stationary environment
- Their attention was attracted towards a focus of expansion, showing its psychological importance
What are affordances?
Along with moving around our surroundings (optic flow), Gibson also emphasized affordances
- He argued that the potential use (the affordance) of objects is directly perceivable without relying on stored knowledge (top-down processing)
- For example, a chair affords sitting, a mug handle affords grasping (or an orange half may afford squeezing?)
affordances - evidence
- Pappas & Mack (2008) presented images of objects to participants so briefly that they were not consciously perceived (top-down processing could not be engaged)
- Despite this, each object’s main affordance produced a motor response in the brain (e.g., presentation of a hammer activated areas associated with preparing to use a hammer).
- This provides convincing evidence that the potential use of objects –the affordance- is directly perceived (without needing top-down processing
affordances - evidence pt2
- Di Stasi & Guardini (2007) provided evidence of the affordance of ‘climbability’ of steps varying in height.
- The step height judged most climbable was the one that would have involved the minimum expenditure of energy
strengths of gibsons views
•Natural scenes are of fundamental importance too visual perception (Bruce & Tadmor, 2015).
•Gibson was correct in that static visual arrays don’t mimic what we do in real life.
Foulsham & Kingstone (2017) showed that eye fixations were significantly different in real motion (walking around) compared to viewing static images.
•Gibson was ahead of his time in that vision-for-action is a key part of Milner & Goodale’s model (discussed in week 3
limitations
Gibson asserted that perception is “direct” in that we can pick-up information from the optic array directly•
But: It is not specified how this information is “picked up”, so it is a little vague.
•Sometimes it’s useful to try to recognize what something is before carrying out an action.
limits pt2
approach to affordances was oversimplified.•Example: cutting up a tomato involves selecting an appropriate tool, deciding how to hold the tomato etc.
- “People reason about physical object properties to solve everyday life activities” (Osiurak & Badets, 2016, P540).
- This is very different to his assumption of picking up affordance information directly
limits pt3
His view largely ignored the role of stored knowledge in processing
•…he saw no place for top-down processing such as memory and past experience in the processing of visual information
•This represents a vast oversimplification.
